1. Field of the Invention
The present invention relates to a ghost canceler for use in combination with high quality television receivers, etc.
2. Description of the Related Art
In high quality television receivers such as EDTV, IDTV, etc., a television video signal in an NTSC standard format is converted to a digital signal. Once in digital form, the video signal is processed in various ways to improve image quality. This processing of the video signal includes such processing as: 1) line sequential scanning conversion by line interpolation, 2) removal of noises, and 3) compensation of contour.
In such high quality television receivers, a ghost canceler is added to effectively improve upon the above-described various kinds of signal processing to enhance image quality. Ghost cancelers come in two main types. One type is built-in to the television receiver body. Another type is external and coupled to the television. This second type, sometimes referred to as an "adapter type", is coupled to the television receiver, but remains outside the television receiver body.
Conventionally, signals are input and output between a ghost canceler of the adapter type and a television receiver as shown in FIG. 1 (PRIOR ART). Namely, a video signal subjected to a ghost canceling processing is transmitted to a ghost canceler 30 through a signal line 41 from a television receiver 20. Then, a ghost-canceled video signal is returned to the television receiver 20 through a signal line 42 from the ghost canceler 30. Signal lines 41 and 42 share a common ground line 43.
The conventional ghost canceler shown in FIG. 1 (PRIOR ART) only returns its ghost canceled video signal to the television receiver. Therefore, the ghost canceled video signal cannot be directly supplied to a picture recording input terminal of a video tape recorder (VTR) without first passing through the television receiver, which is inconvenient.
There has been one proposed one construction in which an output terminal is provided on the ghost canceler for supplying the ghost-cancelled video signal. In this construction, a video signal can be supplied directly to a VTR. However, even using such a construction, it is necessary to run a separate cable from the television receiver to the VTR to record sound along with the video signal. Therefore, it is necessary to use separate cables for video and sound systems. This makes VTR recording operation somewhat complicated.
Further, the use of an external ghost processor is particularly awkward in case that the use of the ghost canceler is not required. It is necessary to provide, when the ghost canceler is not used, a loop to return the video signal from one part of the television (that would have been coupled to the ghost canceler) to another part of the television (that would have received a signal from the ghost canceler). Thus, there must be a signal loop within the television receiver. Therefore it is necessary to provide a video switching circuit for switching the video signal to flow back into the television when the ghost canceler is not used. This is rather cumbersome.
Also, conditions of ghosts in the television signal are different on each channel. Therefore, when a user switches from one channel to another, the previous ghost canceling function may deteriorate immediately after the channel is changed. At that time, the ghost canceler may cause a video "disturbance" to appear on the television screen that is more irritating to a television watcher than the ghost itself.